The cAMP content of cultured human fibroblasts is increased by incubation of cells with several effectors, e.g., bradykinin, PGE1, isoporterenol, and choleragen. Bradykinin increases production of prostaglandins of the E series and prostacyclin, as measured by radioimmunoassay. Both prostaglandins, in turn, stimulate production of cAMP in cultured human foreskin fibroblasts. Responsiveness to bradykinin is altered by duration of incubation of fibroblasts in serum containing growth medium and by exposure of fibroblasts to agents such as dexamethasone, glutamine, and tryptophan. The effects of these agents can be related to their effects on bradykinin stimulation of prostaglandin production.